Conan O'Brien vs. Jay Leno

O'Brien was tapped to replace Leno on The Tonight Show back in 2009, but in one of the most famous late-night shake-ups ever, he was ousted after just seven months so Leno could take his job back. The fracas proved to be divisive not just for the comedians involved but also for their fellow late-night hosts, many of whom sided with O'Brien. "The odds are we will both leave this Earth without speaking to each other, which is fine," O'Brien said of Leno in 2012. "There's really nothing to say."